Metal oxides, particularly mixed-valent manganites are at the focus of scientific attention in recent times in view of their peculiar properties emanating from a competition between different attendant energies (charge, spin, orbital and lattice).
The high carrier densities in such functional oxide systems are considered a big plus in their potential for future electronics at the nanoscale where silicon based systems face carrier statistics problems. Therefore extensive research work is being done on exploring the properties of hetero-structures and multi-layers involving these and other lattice-matched oxide systems seeking novel phenomena. Recently, some unique, unusual and novel physical properties have been reported in the domains of transport and magnetism in such oxide based interface systems. Uni polar and bipolar switching has been observed in different film and interface systems, and mechanisms based on filamentary path formation or field induced interface barrier modification have been proposed.
Resistive switching (RS) is an especially interesting phenomenon that has attracted recent attention in view of its potential for alternative high density non-volatile memory application. Unipolar and bipolar switching has been observed in different film and interface systems, and mechanisms based on filamentary path formation or field induced interface barrier modification have been proposed [J. Maier, Nature Mater. 4, 805 (2005); R Waser, R Dittmann, G Staikov, and K Szot, Adv. Mater. 21, 2632 (2009)]. In manganites, resistive switching (RS) was first reported in PrxCa1-xMnO3 (PCMO, a charge ordered (CO) insulator) in the hole doping regime (x=0.1-1.0) having lowest bandwidth amongst the manganite family. The melting of the CO state with concurrent appearance of ferromagnetic nuclei under external perturbations (electric/magnetic fields, current, temperature etc) led to a large resistance reduction. Subsequent studies have brought out the significance of interfacial effects in RS in manganites and various related models have also been proposed.
There is one previous report by Das et al [S. Das, S. Majumdar, S. Giri, J. Phys. Chem. C 114, 6671 (2010)] on low field magnetic tuning of RS in very thick (83 nm) sol-gel deposited NiO films but only at low temperature.
An article titled “Room Temperature Magnetic Barrier Layers in Magnetic Tunnel Junctions” by B. B. Nelson-Cheeseman, F. J. Wong et. al in APS Journals, Phys. Rev. B Volume 81, Issue 21 relates to the spin transport and interfacial magnetism of magnetic tunnel junctions with highly spin polarized LSMO and Fe3O4 electrodes and a ferrimagnetic NiFe2O4 (NFO) barrier layer. The spin dependent transport is explained in terms of magnon-assisted spin dependent tunneling where the magnons are excited in the barrier layer itself. Tri layers of LSMO (25 nm)/NFO (3 nm)/Fe3O4 (25 nm) were grown by pulsed laser deposition on (110)-oriented SrTiO3 (STO) substrates. Magnetization is induced at +/−1.5 Tesla and the magnetic field applied is in the range of −2000 to +2000 Oe.
Article titled “Current switching of resistive states in magnetic resistive manganites” by A. Asamitsu discloses crystals of Pr1-xCaxMnO3 (x=0.3) which were melt-grown by a floating-zone method. The crystals showed the switching phenomenon in a much higher magnetic field of approx. 4 tesla.
Though, resistive switching is demonstrated in other metal oxides systems and their interfaces and shown to be tuned under magnetic fields, however the “magnetic” aspect of magnetic oxides has not been emphasized especially in terms of low field tenability.